v3.26.1
Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2025
Mar. 12, 2026
Jun. 30, 2025
Document Information [Line Items]      
Entity Central Index Key 0001602658    
Entity Registrant Name Investar Holding Corporation    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2025    
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Document Transition Report false    
Entity File Number 001-36522    
Entity Incorporation, State or Country Code LA    
Entity Tax Identification Number 27-1560715    
Entity Address, Address Line One 10500 Coursey Blvd.    
Entity Address, City or Town Baton Rouge    
Entity Address, State or Province LA    
Entity Address, Postal Zip Code 70816    
City Area Code 225    
Local Phone Number 227-2222    
Title of 12(b) Security Common stock, $1.00 par value per share    
Trading Symbol ISTR    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 177,300,000
Entity Common Stock, Shares Outstanding   13,750,025  
Auditor Name BDO USA, P.C.    
Auditor Location Baton Rouge, Louisiana    
Auditor Firm ID 243